Construction of chimeric catechol 2,3-dioxygenase exhibiting improved activity against the suicide inhibitor 4-methylcatechol

Molecular cloning, characterization, and structural stability analysis of a rare acidic catechol 2,3-dioxygenase from the metagenome of coal-polluted soil

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous environmental pollutants that pose substantial health hazards, especially in coal-mining areas. This study presented the metagenomic identification and comprehensive characterization of a novel acidic catechol 2,3-dioxygenase, C23O927, derived from a coal-contaminated soil metagenome. Optimal enzymatic activity for C23O927 was observed at pH 4.0 and 55 °C, with remarkable stability across a wide pH spectrum (2.0-10.0) and temperature range (30 °C-60 °C). The enzyme displayed robust tolerance to various organic solvents and salts, and its activity was notably activated by diverse metal ions. Distinct from other catechol 2,3-dioxygenases, C23O927 exhibited oxygen tolerance and maintained robust activity after purification at 4 °C for up to three days. The structural stability of C23O927 is attributed to its unique extended β-sheet structure and increased α-helices. These characteristics help enhance rigidity and reduce the exposure of the hydrophobic core, thereby conferring greater stability on C23O927. The unique properties of C23O927, which include an optimal pH for acidic environments, salt tolerance, resistance to metal ions and organic solvents, and thermal stability, render it a promising candidate for industrial waste management and soil bioremediation.

Biodecomposition of Phenanthrene and Pyrene by a Genetically Engineered Escherichia coli

BACKGROUND

Genetically engineered microorganisms (GEMs) can be used for bioremediation of the biological pollutants into nonhazardous or less-hazardous substances, at lower cost. Polycyclic aromatic hydrocarbons (PAHs) are one of these contaminants that associated with a risk of human cancer development. Genetically engineered E. coli that encoded catechol 2,3- dioxygenase (C230) was created and investigated its ability to biodecomposition of phenanthrene and pyrene in spiked soil using high-performance liquid chromatography (HPLC) measurement. We revised patents documents relating to the use of GEMs for bioremediation. This approach have already been done in others studies although using other genes codifying for same catechol degradation approach.

OBJECTIVE

In this study, we investigated biodecomposition of phenanthrene and pyrene by a genetically engineered Escherichia coli.

METHODS

Briefly, following the cloning of C230 gene (nahH) into pUC18 vector and transformation into E. coli Top10F, the complementary tests, including catalase, oxidase and PCR were used as on isolated bacteria from spiked soil.

RESULTS

The results of HPLC measurement showed that in spiked soil containing engineered E. coli, biodegradation of phenanthrene and pyrene comparing to autoclaved soil that inoculated by wild type of E. coli and normal soil group with natural microbial flora, were statistically significant (p<0.05). Moreover, catalase test was positive while the oxidase tests were negative.

CONCLUSION

These findings indicated that genetically manipulated E. coli can provide an effective clean-up process on PAH compounds and it is useful for bioremediation of environmental pollution with petrochemical products.

Activity of a carboxyl-terminal truncated form of catechol 2,3-dioxygenase from Planococcus sp. S5

Catechol 2,3-dioxygenases (C23Os, E.C.1.13.12.2) are two domain enzymes that catalyze degradation of monoaromatic hydrocarbons. The catalytically active C-domain of all known C23Os comprises ferrous ion ligands as well as residues forming active site pocket. The aim of this work was to examine and discuss the effect of nonsense mutation at position 289 on the activity of catechol 2,3-dioxygenase from Planococcus strain. Although the mutant C23O showed the same optimal temperature for activity as the wild-type protein (35°C), it exhibited activity slightly more tolerant to alkaline pH. Mutant enzyme exhibited also higher affinity to catechol as a substrate. Its K_m (66.17 µM) was approximately 30% lower than that of wild-type enzyme. Interestingly, removal of the C-terminal residues resulted in 1.5- to 1.8-fold (P < 0.05) increase in the activity of C23OB61 against 4-methylcatechol and 4-chlorocatechol, respectively, while towards catechol the activity of the protein dropped to about 80% of that of the wild-type enzyme. The results obtained may facilitate the engineering of the C23O for application in the bioremediation of polluted areas.

Cloning and mutagenesis of catechol 2,3-dioxygenase gene from the gram-positive Planococcus sp. strain S5

In this study, the catechol 2,3-dioxygenase gene that encodes a 307- amino-acid protein was cloned from Planococcus sp. S5. The protein was identified to be a member of the superfamily I, subfamily 2A of extradiol dioxygenases. In order to study residues and regions affecting the enzyme's catalytic parameters, the c23o gene was randomly mutated by error-prone PCR. The wild-type enzyme and mutants containing substitutions within either the C-terminal or both domains were functionally produced in Escherichia coli and their activity towards catechol was characterized. The C23OB65 mutant with R296Q substitution showed significant tolerance to acidic pH with an optimum at pH 5.0. In addition, it showed activity more than 1.5 as high as that of the wild type enzyme and its Km was 2.5 times lower. It also showed altered sensitivity to substrate inhibition. The results indicate that residue at position 296 plays a role in determining pH dependence of the enzyme and its activity. Lower activity toward catechol was shown for mutants C23OB58 and C23OB81. Despite lower activity, these mutants showed higher affinity to catechol and were more sensitive to substrate concentration than nonmutated enzyme.

Biodegradation of aromatic compounds: current status and opportunities for biomolecular approaches

Biodegradation can achieve complete and cost-effective elimination of aromatic pollutants through harnessing diverse microbial metabolic processes. Aromatics biodegradation plays an important role in environmental cleanup and has been extensively studied since the inception of biodegradation. These studies, however, are diverse and scattered; there is an imperative need to consolidate, summarize, and review the current status of aromatics biodegradation. The first part of this review briefly discusses the catabolic mechanisms and describes the current status of aromatics biodegradation. Emphasis is placed on monocyclic, polycyclic, and chlorinated aromatic hydrocarbons because they are the most prevalent aromatic contaminants in the environment. Among monocyclic aromatic hydrocarbons, benzene, toluene, ethylbenzene, and xylene; phenylacetic acid; and structurally related aromatic compounds are highlighted. In addition, biofilms and their applications in biodegradation of aromatic compounds are briefly discussed. In recent years, various biomolecular approaches have been applied to design and understand microorganisms for enhanced biodegradation. In the second part of this review, biomolecular approaches, their applications in aromatics biodegradation, and associated biosafety issues are discussed. Particular attention is given to the applications of metabolic engineering, protein engineering, and "omics" technologies in aromatics biodegradation.

The Ins and Outs of Ring-Cleaving Dioxygenases

Ring-cleaving dioxygenases catalyze the oxygenolytic fission of catecholic compounds, a critical step in the aerobic degradation of aromatic compounds by bacteria. Two classes of these enzymes have been identified, based on the mode of ring cleavage: intradiol dioxygenases utilize non-heme Fe(III) to cleave the aromatic nucleus ortho to the hydroxyl substituents; and extradiol dioxygenases utilize non-heme Fe(II) or other divalent metal ions to cleave the aromatic nucleus meta to the hydroxyl substituents. Recent genomic, structural, spectroscopic, and kinetic studies have increased our understanding of the distribution, evolution, and mechanisms of these enzymes. Overall, extradiol dioxygenases appear to be more versatile than their intradiol counterparts. Thus, the former cleave a wider variety of substrates, have evolved on a larger number of structural scaffolds, and occur in a wider variety of pathways, including biosynthetic pathways and pathways that degrade non-aromatic compounds. The catalytic mechanisms of the two enzymes proceed via similar iron-alkylperoxo intermediates. The ability of extradiol enzymes to act on a variety of non-catecholic compounds is consistent with proposed differences in the breakdown of this iron-alkylperoxo intermediate in the two enzymes, involving alkenyl migration in extradiol enzymes and acyl migration in intradiol enzymes. Nevertheless, despite recent advances in our understanding of these fascinating enzymes, the major determinant of the mode of ring cleavage remains unknown.

Single-turnover kinetics of 2,3-dihydroxybiphenyl 1,2-dioxygenase reacting with 3-formylcatechol

2,3-Dihydroxybiphenyl 1,2-dioxygenase (EC 1.13.11.39) from Pseudomonas sp. strain KKS102 (BphC) catalyzes the proximal extradiol cleavage of the catechol ring of 2,3-dihydroxybiphenyl (DHB), a key step in the biodegradation of polychlorinated biphenyl. Because the active site Fe(II) ion of the extradiol dioxygenase is colorless, it has been difficult to monitor the reaction cycle kinetics. Here, we have found that BphC binds strongly the chromophoric substrate 3-formylcatechol (3FC) as a monoanion (Kd=0.8 microM) and cleaves it two orders of magnitude slower compared to DHB under air-saturation conditions. By utilizing 3FC as a probe, the reaction cycle kinetics of BphC was monitored for the first time. The binding of 3FC occurred in a three-step process involving rapid deprotonation of 3FC. The bound monoanionic 3FC reacted slowly with O2 in three steps, occurring in sequence, the ring opening step being the slowest one.

Accessing microbial diversity for bioremediation and environmental restoration

Biological methods for decontamination promise an improved substitute for ineffective and costly physico-chemical remediation methods, although so far only a fraction of the total microbial diversity (i.e. the culturable fraction with metabolic potential) has been harnessed for this purpose. Exploring and exploiting the "overlooked" genetic resource might ameliorate concerns associated with the degradation of recalcitrant and xenobiotic pollutants that are not degraded or only poorly degraded by known culturable bacteria. Recent advances in the molecular genetics of biodegradation and in knowledge-based methods of rational protein modification provide insight into the development of "designer biocatalysts" for environmental restoration. The application of such genetically engineered microorganisms (GEMs) in the environment has been limited, however, owing to the risks associated with uncontrolled growth and proliferation of the introduced biocatalyst and horizontal gene transfer. Programming rapid death of the biocatalyst soon after the depletion of the pollutant could minimize the risks in developing these technologies for successful bioremediation.

Laboratory evolution of catabolic enzymes and pathways

The laboratory evolution of environmentally relevant enzymes and proteins has resulted in the generation of optimized and stabilized enzymes, as well as enzymes with activity against new substrates. Numerous methods, including random mutagenesis, site-directed mutagenesis and DNA shuffling, have been widely used to generate variants of existing enzymes. These evolved catabolic enzymes have application for improving biodegradation pathways, generating engineered pathways for the degradation of particularly recalcitrant compounds, and for the development of biocatalytic processes to produce useful compounds. Regulatory proteins associated with catabolic pathways have been utilized to generate biosensors for the detection of bioavailable concentrations of environmentally relevant chemicals.

Suicidal genetically engineered microorganisms for bioremediation: Need and perspectives

In the past few decades, increased awareness of environmental pollution has led to the exploitation of microbial metabolic potential in the construction of several genetically engineered microorganisms (GEMs) for bioremediation purposes. At the same time, environmental concerns and regulatory constraints have limited the in situ application of GEMs, the ultimate objective behind their development. In order to address the anticipated risks due to the uncontrolled survival/dispersal of GEMs or recombinant plasmids into the environment, some attempts have been made to construct systems that would contain the released organisms. This article discusses the designing of safer genetically engineered organisms for environmental release with specific emphasis on the use of bacterial plasmid addiction systems to limit their survival thus minimizing the anticipated risk. We also conceptualize a novel strategy to construct "Suicidal Genetically Engineered Microorganisms (SGEMs)" by exploring/combining the knowledge of different plasmid addiction systems (such as antisense RNA-regulated plasmid addiction, proteic plasmid addiction etc.) and inducible degradative operons of bacteria.